Simplify the following expression: $p = \dfrac{1}{2r} + \dfrac{1}{8r}$
Answer: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2r$ and $8r$ $\lcm(2r, 8r) = 8r$ $ p = \dfrac{4}{4} \cdot \dfrac{1}{2r} + \dfrac{1}{1} \cdot \dfrac{1}{8r} $ $p = \dfrac{4}{8r} + \dfrac{1}{8r}$ $p = \dfrac{4 +1}{8r}$ $p = \dfrac{5}{8r}$